Free tools / Calorie Deficit Calculator
Calorie Deficit Calculator
Choose how fast you want to lose weight and get a daily calorie target that gets you there, with guardrails so it stays sensible.
Enter your age, height and weight to see your numbers.
Estimate based on the Mifflin-St Jeor equation. General wellness information, not medical advice.
Numbers are the easy part.
FIIT turns a photo of your meal into calories and macros, then coaches you daily so you actually hit the target.
Free to download · iPhone · Android coming soon
How a calorie deficit works
Fat loss happens when you consistently eat less energy than you burn. A common rule of thumb is that about 7,700 kcal (3,500 kcal per lb) equals one kilogram of body weight, so a 500 kcal daily deficit points toward roughly 0.5 kg (1 lb) a week. It is an approximation, bodies adapt, water weight moves around, but it is a good planning tool.
How fast should you lose weight?
A widely used guideline is 0.5–1% of body weight per week. Slower is easier to stick to and protects muscle; faster is possible early on but hard to sustain. This calculator warns you if your chosen rate goes above 1% of body weight per week or would push you below 1,200 kcal (women) or 1,500 kcal (men).
Make the deficit stick
The number matters less than whether you can follow it for months. Prioritise protein, keep food logging low-friction, and judge progress by your weekly weight trend, not single weigh-ins. FIIT does the logging from a photo and recalculates your target as your trend changes.
Frequently asked questions
How big should my calorie deficit be?
For most people, 300–600 kcal below maintenance (about 15–25%) is a sustainable deficit. Larger deficits increase the risk of muscle loss, low energy and giving up.
Can I lose weight eating 1,200 calories?
Some people can, but it is close to the practical floor for many adults and is not right for everyone. If your calculated target is near or below 1,200 (women) or 1,500 (men), choose a slower rate or speak to a healthcare professional.
Why did I stop losing weight?
As you lose weight your maintenance calories fall, and water retention can mask fat loss for a couple of weeks. Recalculate with your new weight, and look at a 2–3 week trend before changing anything.
FIIT provides general wellness information, not medical advice. Consult a healthcare professional before changing your diet.